Process for concentrating aqueous nitric acid by means of sulphuric acid



Nov. 20,1923. 1,474,647

' W. SIEBERT PROCESS FOR CONCENTRATING AQUEOUS NITRIC ACID BY MEANS OF SULFURIC ACID Filed May 13 1922 Patented Nov-12$, 1923. E

car-ran stares rarsarcraica.

WERNER sxnnnn'r, or LAUFENBURG, AARGAU, SWI'IZERLAND, Assic-non T NITRUM AKTIENGESELLSCHAFT, or ZURICH, SWITZERLAND, A cosroaa'rron or SWITZER- LAND. c

PROCESS FOR CONCENTRATING AQUEOUS NITRIC ACID BY MEANS Q1 SULPHURIG ACID.

Application filed May 13, 1922. Serial No. 560,725.

To allwkom it may ooncem: in such a manner that only fumes of a con- Be'it known that I, VERNER Srnsnn'r, a centration of 97% and above pass further 55 citizen of the Republic of Germany, residon. while the weak acid flows back into the ing at Laut'enburg, Aargau, Switzerland, retort. The application of the process un- 5 have invented a certain new andusefi'il Imdcr vacuum allows rctorts to be employed provement in a Process for Concentrating which have coils-or the-like cast in the body.

Aqueous Nitric Acid by Means of Sulphuric of the retort which coils can be heated with Acid, of which the following is a specificasteam at a pressure of 5 to 8 atmospheres. tion, reference being bad therein to the ac- The novel process has the great advantage 10 companying drawing. I "over the hitherto known processes that the The invention consists -in an improved whole amount of nitric acid is'obtained in process for concentratingaqueous nitric acid a highly concentratedform with the smallest Q5 by'means of sulphuric acid. quantity of sulphuric acid. Dilute nitric aci'd'obtain'ed by the absor Thus less sulphuric acid is required in tion of nitrous fumes has been concentrated this' process than when introducing steam with the aid of sulphuric acid on a large directly into the acid mixture and at the scale. Because of the importance of the same time the condensation of the nitrous process quite a number of. different methods fumes is not impeded by inert gases. have been tried in which a mixture of dilute In the accompanying" drawing an example nitric acid and sulphuric acid is treated of an installation for carrying the improved with steam and inert gases in towers or 001- process according to the invention into ef-. umns whereby the nitric acid fumes-are defeet is diauramma-tically illustrated. I prived of water by the sulphuric acid. In this drawing 1 denotes the cast iron The addition of steam increases, however, boiler or retortprovided with coils 2'which. the consumption of sulphuric acid per unit may be cast into the wall of the retort. T0 of HNO which makes it necessary to inthese coils 2 steam is supplied for heating stall much larger apparatus for reconcenthe mixture of dilute nitric acid and sulhating the sulphuric. acid. In order to phuric acid contained in the retort 1. For .avoid the introduction of steam into the the purpose of increasing the temperature acid mixture it' has already been suggested the steam may be supplied'at a temperature to distill the nitric acid outof the mixture of 5 to'8 atmospheres. The. nitric acid in iron pans or receptacles externally heated. fumes emanating from the heated liquid This common process presents the great mixture in retort l are led through the con-' disadvantage that the concentration of the duit 3 into dephlegmator 4- in which the nitric acid diminishes constantly from the separation of the nitric acid t'umes accordbeginning of the process to the end. ing to the concentration ta kcs place. Fumes Atthe beginning of the distillation it is, of a. concentratiou'ot 97% and above pass 90 for example, possible to produce HNO of further on into the condenscrfi and the a concentration of 95%, but towards the end liquid nitric acid is collected in receptacles 6.

.of the process the concentration drops to The nitric acid fumes having a concenabout which makes it necessary to retration of below 97% cannot pass the peat the distillation. v dephlcgmator and are returned into the Now in the present invention it has been, boiler 1 where they are, again subjected to found that it is possible to recover the whole the distilling action. 7 denotes a vacuum amount of the introduced HNO, as acid of pump for maintaining a vacuum, in the a concentration offrom 97 to 99% by diswhole system. tilling the acid under vacuum in a sort of a I claim: cast iron boiler or retort and by inserting a 1. The process for concentrating aqueous dephlegmator between the distillation retort nitricacid bynieans of sulphuric acid which 5 and the condensing apparatus; this dephlegconsists in distilling a mixture of dilute mator being kept at a temperature of about nitric acid and sulphuric acid under vacuum, 60C. In the dephlegmator the nitric acid dephlegmating' the nitric acid fumes, re- 105 fumes coming from the retort are separated turning for further distillation the fumes which have low concentration, and condensing'the fumes which have high concentration.

2. An apparatus for concentrating aqueous nitric acid by means of sulphuric acid,

comprising a retort for distilling nitric acid fumes from a mixture of aqueous nitric acld and. sulphurlc acid, a condenser, a

dephlegmator inserted between the retort and the condenser to return the fumes of 10 low concentration to the retort and deliver to the condenser the fumes of high concentration, and means to maintain a vacuum in the apparatus.

In testimony whereof I affix my si nature.

DR. \VERNER SIEB RT. 

